Thermionic valve circuits



. M. M. LEVY TH'EBMIONIC VALVE CIRCUITS Jan. 27, v1943.

Filed Jan. 18, 1944 HG2. im

VOLTAGE VAR/770V FROM NORM/IL F/GB.

m. @wwf m RC .I ...Ik 3,@ A Hm Patented Jan. 27, 1948 THERMIONIC VALVE CIRCUITS" Maurice Moise Levy, London, England, assigner,y by mesne assignments, to. International Standard Electric Corporation, New York, N. Y., a

corporation of Delaware Application JanuarylS, 1944, Serial No. 518,703 In GreatBx-itain Januaryv 29, 19513.

1,0., Claims.

The present invention relates to thermionic valve circuits and in particular to means for stabilizing the operation of` such circuits against variations of the operating voltages.

The principal cause of variation ofV the-performance of thermionic valve circuits is variation in the voltage of the anode-supplyv source. This produces changes in gain,ror rectifying effect (or the like), in the valves, due mainly to the changes in the anode currents whichk occur. Previous stabilizing circuit arrangements havel generally suffered from the disadvantage that they greatly increase the load on theV high tension supply source. The principal object of thepresent invention is to provide an arrangement by which a high degree of stabilization isolotained, but which at the same time increases the load on the supply source by only a smallfraction. According to the invention, there is provided an arrangement for stabilizing the-operation oran electrical circuit which circuit includes one or more thermionic Valves supplied with current from a source of variable voltage, comprising means for applying to agrid of the said Valve or each of them a potential varying in such afmanner as `to render the performance characteristic or characteristics of the electrical circuit substantially unaffected by the said voltagevariation.

Accordingto another aspect the invention may comprise an arrangement for stabilizing theA operation of an electrical circuit, which circuit includes one or more thermionic valvessupplied with anode currentr from. a high-tension source of variable voltage, comprising astabilizing thermionic Valve to which the voltage variationsof the source are applied, means beinglprovided for applying to a grid in each of the said-one or more valves a voltage derived from the anode-cathode circuit of the stabilizing valve and adapted to vary in such manner as to .maintain substantially constant the performance characteristic or characteristics of the electrical circuit.

The invention will be. described with reference to the accompanying drawing in which- Fig. 1 shows curvesshowing the effect on the anode current of variations inA the Voltage applied to the electrodes of a thermionic valve.

Fig. 2 shows the current supply arrangements for such a valve, and

Figs. 3 and 4 show schematiccircuit diagrams of two embodiments of the invention.

The principle of theinvention will beunderstood from the following explanation. In amultigrid valve the anode current varies by only a.

small amount when the anode voltage varies, but

varies considerably with the voltage ofthe control gridor ofthe screen grid. Thisis illustrated in Fig. l which applies to a certaintypeof pentode valve operated according to the following table:

Normal anode potential; volts 200 Normalscreen grid potential do Normal control grid potentialdo -8 Anode current with above potentials milliamps 50 Mutual conductance; micromhos-- 9000 In Fig. 1, the linesA andB represent the eff fectj onthe anode current of changes in the-anode and' screen grid voltages, respectively. The eff ect of changes inthe control grid voltage isfnot shown, and on the scale, of this ligure it would be represented by a, line much. steeper than the line B.k Theline C represents the eiect of changingl the applied high tension voltage the normal value of which is,250 volts when the valve is ar,- ranged in the circuit shown in Fig. 2, in` which the resistances had, the values R1=1,000 ohms, R2=70, 000 ohms and R3=150 ohms.. In this case changingthe applied high tension Voltage changes the anode end'screen grid voltages inthe same direction, and the control gridvoltagein the opposite directiomthe net result being toproduce a curve C which is several times steeper than. A. The circuit of Fig. `21 represents an actual arrangement for supplyingA and biassingV the valve in a practical circuit,kso` thatthe curve C shows the totalresultant effect of variations in the anode supply voltage on the anode current. According to the invention the anode current varia.- tions are counteracted by applying to one ofthe grids an oppositely, varyingV voltagey derived from the varying supply voltage andv proportioned so that the anode currentremains substantially. constant, or varies so that theA performance ofthe valve, or that of thecircuit of which it forms a part, remains substantially unaffectedby the variations in the supply voltage. It will be understood, of course,y that specific gures have been quoted for the. sake of clearness, but the invention is applicable to valves having other characteristics supplied in any convenient way.

InFig. 3 is shown one embodiment of the4 invention applied to an.` amplier having two'valve stages. which comprise respectively two pentodes V1` and V2 arranged as shown in Fig. 2-and hav.- ing the characteristics given above. The-amplier may have other valve stages (not shown) which may or may not lie-stabilized according to this-invention. The anodefof V1 is coupledv to the control grid of V2 through an appropriate blocking condenser K. Each valve has an appropriate grid leal: resistance G. Connection is made to earlier stages (if any) at terminal l, and to later stages (if any) at terminal 2. These other stages are not shown in Fig. 3, and may be provided in any appropriate way.

The screen grid voltages for the two Valves V1 and V2 are derived from a stabilizing valve V which is preferably, but not essentially, a pentode as shown. The stabilizing valve is provided with an adjustable anode resistance R4, and a resistance R is connected in series with the cathode. The screen grid is polarized from the high tension supply through an appropriate resistance Re.

The variations of the high tension Voltage are communicated to the control grid of Vo by means of a potentiometer consisting of three (or other appropriate number) of neon discharge tubes N1, N2, N3 (or other like gas-filled tubes) and a resistance R1. These tubes produce a substantially constant difference between the control grid voltage and the voltage of the high tension supply so that the variations of the later are applied to the control grid without any reduction in amplitude; the actual voltage applied to the control grid is however only a fraction of the high tension voltage.

The screen grids of the valves V1 and V2 are connected to adjustable tapping points on the adjustable resistance R4 through resistances Ra and R9, and accordingly they derive their voltage from the anode voltage of the stabilizing valve Vo.

The stabilizing pentode Vo can be a low power Valve, whose anode current should preferably be of the same order as the sum of the screen currents of the valves which it is designed to stabilize. The resistance R5 should be a relatively high resistance so that the control grid potential changes are substantially transferred to the cathode. Let it be supposed that the high tension supply Voltage increases by a small amount v. The control grid voltage of the valve Vu will increase by o on account of the action of the neon tubes, and so substantially also will the cathode voltage. This rise in the cathode voltage is due to an increase in the cathode current, part of which passes through the resistance R4. This resistance should be larger than R5 (for example R2=about 2R5) and it will be possible to find a point on Ri, probably rather near the anode end, the potential of which is unchanged by the increase v, because the increased potential drop in the resistance due to the increased anode current is equal to v thus compensating for the increase of the high tension voltage. If the screen grid of the valve V1 for example, should be connected to this point, the screen grid potential will remain constant; however, in orderto compensate for the increased high tension voltage it is necessary to cause the screen grid potential to be reduced by a very small amount. In other words the screen grid must be connected to a point on R4 whose potential decreases slightly as a result of the increase in o. This point will be slightly nearer the anode of Vo than the first mentioned point. In practice, of course, the proper point will be found by trial, R4 having been chosen suiliciently large to allow this to be done.

In the particular case shown in Fig. 3, the two valves V1 and V2 are supposed to be of the same type so that the adjustment for both of them would be practically the same. It is therefore possible to simplify the circuit slightly by connecting Rs and R2 both to the anode of Vo, instead of to the tapping point and to adjust the value of R4 until the desired compensation is obtained.

In one practical circuit according to Fig. 3, the valves V1 and V2 were of the kind specied above in connection with Fig. 2, the high tension Voltage being 250 volts. The valve Vo was a pentode supplying an anode current of about 5 milliamps, the screen current being about 2 milliamps. The resistance Rs was 5,000 ohms, Re was zero and R4 had a, maximum value of about 10,000 ohms. Re and R9 were each 10,000 ohms. This produces an anode voltage of about 130 and screen voltage of 250 for Vn, and screen voltage of for the valves V1 and V2.

The neon tubes N1, N2 and N3 together produce a voltage drop of about 215 volts, and R7 was chosen to be 100,000 ohms, so that the current through the neon tubes was about 0.35 milliamp, the control grid voltage of Vo being about 35.

The total current taken by the two Valves Vi and V2 from the high tension source is about 104 milliamps (including the screen currents) and the additional current taken by the valve Vo is about 9 milliamps including the screen current and the current through the neon tubes. The increase in load due to stabilization is thus quite inconsiderable.

The number of neon tubes such as N1, N2, N3 (or other gas discharge tubes) which are required in the general case depends on the value of the high tension voltage. In the particular circuit according to Fig. 3 which has just been described, each neon tube maintains a constant potential difference of about 70 volts, and the number used should preferably be the maximum consistent with obtaining the constant potential diierence across each one. The remaining drop is taken up by the resistance Rv. By this means the maximum reduction in the high tension voltage is obtained, without reducing the variations.

It is, of course, not essential to use the maximum number of neon tubes, or even to use any at all; and in such a case the control grid of Vo should be connected to an appropriate tapping point on Rv from which it Will obtain a suitable potential. However, if fewer than three neon tubes are used, only a fraction of the high tension voltage variations will be available at the control grid of Vo, and the resistance R4 will have to be increased in order to obtain the same stabilizing eifect.

With the example of Fig. 3 described above, it was found that the high tension voltage could be varied between about 220 volts and 310 volts without producing any appreciable change in the total load current. For this change in voltage the screen voltage of the stabilized valves changes by about 1 volt in the opposite direction.

It should be noted that the resistance R5 provides considerable negative feedback for the valve Vo so that the stabilizing effect will be rendered substantially independent of variation in this valve. The mutual conductance g of the valve used in the above example is about 6,500 micromhos so that variations are reduced by the factor 1/(1+gR5) :about 0.03, using the value 5,000 ohms for R5. Variations are accordingly reduced to 3% and it was found that the valve Vo could be replaced by any other of the same type without ailecting the stabilizing action.

It will be understood, of course. that the number'of valves which may be stabilized in this way is notv limited to two: any number of additional valvesmay be controlled from the same stabilizeA ing valve provided the latter is designed in accordancei with the total screen current as exe plained above. The stabilized valves can be of different types and may be employed as ampliers or oscillators or modulators and not necessarily in the same circuit, the particular amplifying arrangement shown in Fig. 3 being given sirnply as one example.

Fig. 4 shows another form of the invention in which the stabilizing voltage variations are applied to the control grids of the valves V1 and V2 instead'of to the screen grids. Those elements which are the same as in Fig. 3 and have the same functions are given the same designations and will not be again described.

The screen grids of V1 and Vzlare polarized directly from the high tension supply through resistances R2 which may be the same as in Fig. 2. The anode voltage of Vo is stepped down by means of a neon tube N4, for example, similar to N1, N2 and N3 connected in series with a tapped resistance R10. In this case only one neon tube is required, since the anode voltage is about 130 volts: if it exceeded 140 volts two or more might be employed. If other types oi gas lled tubes are used, the number required is determined by the same considerations explained above with reference to N1, N2 and N3.

The control grids of the valves V1 and V2 are connected to the tapping points on R as indicated, which are adjusted to obtain the desired compensation. The resistances R3 may be made adjustable so that appropriate grid .bias may be at the same time obtained.

The action of the circuit of Fig. e is in principle the same as that of Fig. 3, the only difference being that the compensating variations of the control grid voltage will be rather smaller than those of the screen grid voltage to produce the same result. On this account it is probable that two valves of the same type will practically always require diierent adjustments of the tapping points on the resistance Rio.

It will be evident that the arrangement of Fig. 4 is applicable to the stabilizing of triode valves not having any additional grids. As already mentioned, also, the stabilizing valve Vo in either Fig. 3 or Fig. 4 may also be a trio-de, in which case Re is not needed. It will be further evident that if the elements N4 and R10 be added to Fig. 3 in the manner shown in Fig. 4, the valve Vo can be used to stabilize at the same time one group of valves by means of the screen grids, and another group by means of the control grids.

Although the changes in the anode currents of the valves consequent on the variations of the high tension voltage are the principal cause of variation of the performance of the amplier, modulator, or oscillator (or other electrical circuit) of which they form a part; and although the stabilization arrangements described tend to maintain the anode currents constant; actually the ultimate criterion of the operation is some performance characteristic of the circuit, and the adjustments will generally be made so that this characteristic is unaiected by the variations.

For example, the frequency and/or the output of a thermionic valve oscillator may be changed by variations in the high tension supply voltage. It will probably be found that the frequency and the output can both be approximately stabilized by an appropriate adjustment of the arrangement according to the invention,.which'adjustment approximatelyr stabilizes the anode currents of,` one or more of. the valves. However., it may be found that different adjustments are required to stabilize exactly the frequency and the output of the oscillator; and. if there are several valves, both the frequency and the outputV could probably be simultaneously stabilizedby suitable separate adjustments of the oscillating andamplifying valve.

What is claimed is:

1. In an electric circuit, a source of power of variable voltage, at least one thermionic valve having input and output circuits, the output circuit being supplied with current from said source, a separate stabilizing amplifier having an input circuit supplied with a potential varying with said variable voltage, and an output circuit controlling the input circuit of said thermionic valve so as to render its output substantially independent of said variable voltage.

2. A circuit according to claim 1, whereinsaid source of variable voltage is a high tension source and said stabilizing amplier is another thermionic valve having an anode-cathode circuit, the rst-mentioned thermionic valve having an anode supplied fromv said high tension source, and a grid supplied with a potentialderived from said anode-cathode circuit.

3. In an electric circuit, a source of power of variable voltage, at least one thermionic valve having input and output circuits, the output circuit being supplied with current from said source, a separate stabilizing amplier having an input circuit supplied 'with a potential varying with said variable voltage, wherein said source of variable voltage is a high tension source and said stabilizing amplier is another thermionic valve having an anode-cathode circuit, said first-mentioned thermionic valve having a screen grid supplied with a potential derived from said anodecathode circuit.

4. In a circuit according to claim 3, a number of thermionic valves, each one of which has a screen grid, and means for deriving a potential from the output circuit of said stabilizing amplier and applying at least a portion of said potential to said screen grids.

5. A circuit according to claim 1, wherein the output circuit of said stabilizing amplier includes a load resistance and said thermionic valve includes a grid, said grid being connected to a predetermined point on said load resistance.

6. A circuit according to claim 3, wherein said source of variable voltage is a high tension source and said thermionic valve has a screen grid, said stabilizing amplier including a thermionic valve having an anode, said screen grid being supplied with a voltage derived from said anode, said stabilizing amplifier further including means for applying to said screen grid a certain fraction of the anode voltage and a larger fraction of the variations of the anode voltage.

7. A circuit according to claim 3, wherein the output circuit of said stabilizing amplifier includes an anode and a load resistance connected thereto, and said thermionic valve includes a screen grid, said screen grid being connected to a predetermined point on said load resistance, and wherein said output circuit further includes means for applying to said screen grid a certain fraction of the anode voltage and a larger fraction of the variations of said anode voltage.

8. In a circuit according to claim 1, another thermionic valve having anode and cathode, at

least one gas discharge tube and a resistance connected in series between said anode and cathode, said first-mentioned thermionic valve having a control grid connected to a point on said resist ance.

9. A circuit according to claim 3, wherein said source of variable voltage is a high tension source and said stabilizing amplier is another thermionic valve having a control grid and an anodecathode circuit, said first-mentioned thermionic valve having a screen grid supplied with a voltage derived from said anode-cathode circuit, said stabilizing amplier including means for applying to the screen grid of said other thermionic valve a certain fraction of said variable voltage and a larger fraction of the variations thereof.

10. In a circuit according to claim 3, wherein said thermionic valve has an input grid and an anode current derived from said source of variable D. C. voltage, another thermionic valve having a grid circuit and an anode-cathode circuit, means for applying to said grid circuit said variable voltage, means for applying to the input grid of said first-mentioned thermionic valve a voltage derived from said anode-cathode circuit so as to maintain said anode current substantially independent of said variable voltage, said means including at least one gas discharge tube and a resistance in series therewith and connected across said source of variable voltage, said source of variable voltage having a negative terminal connected to said resistance and said other thermionic valve having a grid connected to said resistance at a. tapping point thereof.

MAURICE MOISE LEVY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

